1. Field of the Invention
The present invention relates to a method for manufacturing an optical fiber coupler.
2. Description of the Related Art
An optical fiber coupler is a device for branching/coupling light among a plurality of optical fibers. At present, a fusion-elongation method is regarded as the most suitable method to manufacture an optical fiber coupler with single-mode optical fibers. In this fusion-elongation method, for example, the coatings of two optical fibers are removed in their predetermined sections so as to expose their bare fiber portions, and the bare fiber portions are heated to be fused while being brought into tight contact with each other by twisting or closely arranging in parallel with each other. Thereafter, a constant tension is given to the fused portion while its branching ratio is measured, and the fused portion is heated and elongated. When the branching ratio reaches a desired valve, the elongating is stopped, and the optical fibers are fixed to a protective member.
In the method for manufacturing an optical fiber coupler in which optical fibers are elongated while constant tensions are given thereto in such a manner as mentioned above, it is important to advance the elongating at a speed near a target elongating speed in order to obtain desired characteristics, or in order to prevent the optical fiber from being broken off because of excessive elongating. When the control of the elongating speed is not satisfactory, not only is it impossible to obtain desired characteristics, but also other problems occur, such as breaking of the optical fibers or the like. In addition, when the control is excessive, there is a problem that the elongating is not advanced, the elongating speed vibrates centering the target speed, or the like.